Method and apparatus for transmitting and receiving narrowband synchronization signals

ABSTRACT

This closure relates to narrowband communication supporting an Internet of Things (IoT) service in a next-generation wireless communication system and, more particularly, to a method and apparatus for transmitting and receiving narrowband synchronization signals. A base station transmits a narrowband secondary synchronization signal indicating a narrowband cell identity, a specific sequence generated by performing phase rotation with respect to a base sequence generated through a second Zadoff-Chu sequence having a predetermined length L in a frequency domain and multiplying the base sequence by a cover sequence in element units is used for the narrowband secondary synchronization signal, and a specific root index is selected from among M (M&lt;L) root indices as a root index of the second Zadoff-Chu sequence and the specific root index is selected in a range from k to k+M−1 in terms of a predetermined offset k.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119(e), this application claims the benefit ofU.S. Provisional Patent Application Nos. 62/290,892, filed on Feb. 3,2016, 62/296,592, filed on Feb. 17, 2016, 62/305,543, filed on Mar. 9,2016, 62/315,675, filed on Mar. 31, 2016 and 62/318,801, filed on Apr.6, 2016, and 62/321,702, filed on Apr. 12, 2016, the contents of whichare all hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to narrowband communication supporting anInternet of Things (IoT) service in a next-generation wirelesscommunication system and, more particularly, to a method and apparatusfor transmitting and receiving narrowband synchronization signals.

Discussion of the Related Art

Recently, demand for IoT technology has increased and narrowband IoT(NB-IoT) technology has been discussed in order to support such an IoTservice. NB-IoT seeks to provide appropriate throughput betweenconnected apparatuses despite low apparatus complexity and low powerconsumption.

In 3GPP of the NB-IoT standards, NB-IoT technology capable of beingcombined with other 3GPP technologies such as GSM, WCDMA or LTE has beenstudied. To this end, a resource structure which will be used from theviewpoint of a legacy system has been discussed.

FIG. 1 is a diagram illustrating three modes which may be used inNB-IoT.

In order to satisfy the above-described demand, in NB-IoT, a channelbandwidth of 180 kHz is being considered for use both on uplink anddownlink, which corresponds to one physical resource block (PRB) in anLTE system.

As shown in FIG. 1, NB-IoT may support three modes such as standaloneoperation, guard band operation and inband operation. In particular, inthe inband mode shown in the lower side of FIG. 1, NB-IoT operation maybe performed through a specific narrowband in an LTE channel bandwidth.

In addition, in NB-IoT, using an extended DRX cycle, half-duplex FDD (HDFDD) operation and a single receive antenna in a wireless apparatussubstantially reduce power and cost.

SUMMARY OF THE INVENTION

Accordingly, the present disclosure is directed to a method andapparatus for transmitting and receiving narrowband synchronizationsignals that substantially obviate one or more problems due tolimitations and disadvantages of the related art.

Transmission of narrowband (NB) synchronization signals is necessary forthe above-described NB-IoT operation. Operation in a specific narrowbandis required for NB-IoT operation as shown in FIG. 1. Therefore, there isa need for a method of more efficiently transmitting primarysynchronization signals (PSSs) and secondary synchronization signals(SSSs).

Additional advantages, objects, and features of the disclosure will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of thedisclosure. The objectives and other advantages of the disclosure may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the disclosure, as embodied and broadly described herein, amethod of, at a base station, transmitting a narrowband synchronizationsignal to one or more user equipments (UEs) in a wireless communicationsystem includes transmitting a narrowband primary synchronization signalusing a first Zadoff-Chu sequence having a predetermined root index andtransmitting a narrowband secondary synchronization signal indicating anarrowband cell identity. A specific sequence generated by performingphase rotation with respect to a base sequence generated through asecond Zadoff-Chu sequence having a predetermined length L in afrequency domain and multiplying the base sequence by a cover sequencein element units is used for the narrowband secondary synchronizationsignal, and a specific root index is selected from among M (M<L) rootindices as a root index of the second Zadoff-Chu sequence and thespecific root index is selected in a range from k to k+M−1 in terms of apredetermined offset k. It is noted that multiplying two sequences inelement units (or element by element) means that each one of a pluralityof first elements of the first sequence is multiplied by acorresponding, respective one of a plurality of second elements of asecond sequence to thereby obtain a third sequence, which may be used inorder to generate, for example, a narrowband secondary synchronizationsignal.

The base sequence may have a length N greater than the length L bycyclic extension of the second Zadoff-Chu sequence having the length L.

The N elements of the specific sequence may be mapped to and transmittedin a plurality (P) of orthogonal frequency division multiplexing (OFDM)symbols in the frequency domain a plurality (Q) of elements by aplurality of elements, and P*Q=N.

P may be 11, Q may be 12 and N may be 132.

L may be 131, M may be 126 and k may be 3.

The second Zadoff-Chu sequence may be S_(ZC)(u, n)=exp (jΠun(n+1)/L),where n=0, . . . , 130, L=131, where u denotes the root index of thesecond Zadoff-Chu sequence and satisfies u∈{3, . . . , 128}.

The cover sequence may be a Hadamard sequence having a length R equal toor less than L.

One of four Hadamard sequences may be selected as the cover sequence,wherein the four Hadamard sequences include 0^(th), X-th, Y-th and Z-thHadamard sequences having the length R, and wherein the X-th, Y-th andZ-th Hadamard sequences do not correspond to first, second and thirdHadamard sequences having the length R.

The narrowband synchronization signal may be transmitted in order toperform Internet of Things (IoT) communication operation through anarrowband corresponding to a part of a system bandwidth of the wirelesscommunication system.

In another aspect of the present disclosure, a method of, at a userequipment (UE), receiving a narrowband synchronization signal from abase station in a wireless communication system includes receiving anarrowband primary synchronization signal configured in the form of afirst Zadoff-Chu sequence having a predetermined root index; andreceiving a narrowband secondary synchronization signal indicating anarrowband cell identity. A specific sequence generated by performingphase rotation with respect to a base sequence generated through asecond Zadoff-Chu sequence having a predetermined length L in afrequency domain and multiplying the base sequence by a cover sequencein element units may be used for the narrowband secondarysynchronization signal, and a specific root index may be selected fromamong M (M<L) root indices as a root index of the second Zadoff-Chusequence and the specific root index may be selected in a range from kto k+M−1 in terms of a predetermined offset k.

The base sequence may have a length N greater than the length L bycyclic extension of the second Zadoff-Chu sequence having the length L.

The N elements of the specific sequence may be mapped to and transmittedin a plurality (P) of orthogonal frequency division multiplexing (OFDM)symbols a plurality (Q) of elements by a plurality of elements in thefrequency domain, and P*Q=N.

The second Zadoff-Chu sequence may be S_(ZC)(u, n)=exp (jΠun(n+1)/L),where n=0, . . . , 130, L=131, where u denotes the root index of thesecond Zadoff-Chu sequence and satisfies u∈{3, . . . , 128}.

In another aspect of the present disclosure, a base station fortransmitting a narrowband synchronization signal to one or more userequipments (UEs) in a wireless communication system includes a processorconfigured to generate a narrowband primary synchronization signal usinga first Zadoff-Chu sequence having a predetermined root index and togenerate a narrowband secondary synchronization signal indicating anarrowband cell identity and a transceiver configured to transmit thenarrowband primary synchronization signal and the narrowband secondarysynchronization signal generated by the processor to the one or moreUEs. The processor generates the narrowband secondary synchronizationsignal using a specific sequence generated by performing phase rotationwith respect to a base sequence generated through a second Zadoff-Chusequence having a predetermined length L in a frequency domain andmultiplying the base sequence by a cover sequence in element units, anda specific root index is selected from among M (M<L) root indices as aroot index of the second Zadoff-Chu sequence and the specific root indexis selected in a range from k to k+M−1 in terms of a predeterminedoffset k.

In another aspect of the present disclosure, a user equipment forreceiving a narrowband synchronization signal from a base station in awireless communication system includes a transceiver configured toreceive a narrowband primary synchronization signal configured in theform of a first Zadoff-Chu sequence having a predetermined root indexand receive a narrowband secondary synchronization signal indicating anarrowband cell identity and a processor configured to process thenarrowband primary synchronization signal and the narrowband secondarysynchronization signal received by the transceiver. A specific sequencegenerated by performing phase rotation with respect to a base sequencegenerated through a second Zadoff-Chu sequence having a predeterminedlength L in a frequency domain and multiplying the base sequence by acover sequence in element units is used for the narrowband secondarysynchronization signal, and the processor detects a specific root indexamong M (M<L) root indices as a root index of the second Zadoff-Chusequence and the specific root index is detected in a range from k tok+M−1 in terms of a predetermined offset k.

According to the present invention, it is possible to more efficientlytransmit and receive a synchronization signal for NB-IoT operation in anext-generation wireless communication system.

It is to be understood that both the foregoing general description andthe following detailed description of the present disclosure areexemplary and explanatory and are intended to provide furtherexplanation of the disclosure as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the disclosure andtogether with the description serve to explain the principle of thedisclosure. In the drawings:

FIG. 1 is a diagram illustrating three modes which may be used inNB-IoT;

FIGS. 2 and 3 are diagrams showing a method of transmittingsynchronization signals in the case of using a normal CP and an extendedCP;

FIG. 4 is a diagram showing two sequences in a logical regioninterleaved and mapped in a physical region;

FIG. 5 is a diagram showing the overall structure in whichsynchronization signals are transmitted and received in an NB LTEsystem;

FIG. 6 is a diagram illustrating a method of repeatedly transmitting anNB-PSS in a plurality of OFDM symbols according to an embodiment of thepresent invention;

FIG. 7 is a diagram showing correlation properties of a pair oflength-10 complementary sequences a(n) and b(n) and various c(n)patterns;

FIG. 8 is a diagram illustrating the concept of transmitting an NB-SSSaccording to an embodiment of the present invention;

FIG. 9 is a diagram illustrating a method of generating and transmittingan NB-SSS according to an embodiment of the present invention;

FIG. 10 is a diagram illustrating a method of selecting root indices ofa ZC sequence to be used in an NB-SSS according to an embodiment of thepresent invention;

FIG. 11 is a diagram showing a cross correlation value when a specificHadamard sequence is used in an NB-SSS in one embodiment of the presentinvention;

FIG. 12 is a diagram showing an example of a downlink (DL)/uplink (UL)slot structure in a wireless communication system;

FIG. 13 is a diagram showing a downlink subframe structure used in awireless communication system; and

FIG. 14 is a block diagram showing the components of a transmittingdevice 10 and a receiving device 20 for performing embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description set forth below in connection withthe appended drawings is intended as a description of exemplaryembodiments and is not intended to represent the only embodimentsthrough which the concepts explained in these embodiments can bepracticed.

The detailed description includes details for the purpose of providingan understanding of the present invention. However, it will be apparentto those skilled in the art that these teachings may be implemented andpracticed without these specific details. In some instances, well-knownstructures and devices are omitted in order to avoid obscuring theconcepts of the present invention and the important functions of thestructures and devices are shown in block diagram form.

As described above, the present invention relates to a method oftransmitting and receiving narrowband synchronization signals for NB-IoToperation. Since synchronization signals of an LTE system may be reusedas the synchronization signals for NB-IoT operation, the synchronizationsignals (SSs) of the LTE system will be described in detail, prior totransmission and reception of the NB synchronization signals.

FIGS. 2 and 3 are diagrams showing a method of transmittingsynchronization signals in the case of using a normal CP and an extendedCP.

The SS includes a PSS and an SSS and is used to perform cell search.FIGS. 2 and 3 show frame structures for transmission of the SSs insystems using a normal CP and an extended CP, respectively. The SS istransmitted in second slots of subframe 0 and subframe 5 inconsideration of a GSM frame length of 4.6 ms for ease of inter-RATmeasurement and a boundary of the radio frame may be detected via anSSS. The PSS is transmitted in a last OFDM symbol of the slot and theSSS is transmitted in an OFDM symbol located just ahead of the PSS. TheSS may transmit a total of 504 physical layer cell IDs via a combinationof three PSS and 168 SSSs. In addition, the SS and the PBCH aretransmitted in 6 RBs located at the center of the system bandwidth andmay be detected or decoded by the UE regardless of transmissionbandwidth.

The transmit diversity scheme of the SS uses a single antenna port andis not separately defined in the standard. That is, single antennatransmission or a transmission method (e.g., PVS, TSTD or CDD)transparent to a UE may be used.

Meanwhile, hereinafter, processes of encoding a PSS and an SSS will bedescribed.

In a PSS code, a length-63 Zadoff-Chu (ZC) sequence is defined in thefrequency domain and is used as a sequence of a PSS. The ZC sequence isdefined by Equation 1 and a sequence element n=31 corresponding to a DCsubcarrier is punctured. In Equation 1 below, Nzc=63.

$\begin{matrix}{{d_{u}(n)} = e^{{- j}\frac{\pi\;{{un}{({n + 1})}}}{N_{ZC}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

The remaining 9 subcarriers of 6 RBs (=72 subcarriers) of the centerpart are always transmitted with a value of 0 and cause a filter forperforming synchronization to be easily designed. In order to define atotal of 3 PSSs, in Equation 1, values of u=25, 29 and 34 are used. Atthis time, 29 and 34 have a conjugate symmetry relation and thuscorrelations therefor may be simultaneously performed. Conjugatesymmetry means a relation of Equation 2 below. Using these properties, aone-shot correlator for u=29 and 34 may be implemented and a totalcomputational load may be reduced by about 33.3%.d _(u)(n)=(−1)^(n)(d _(N) _(ZC) _(−u)(n))*, when N _(ZC) is even number.d _(u)(n)=(d _(N) _(ZC) _(−u)(n))*, when N _(ZC) is oddnumber.  Equation 2

Next, encoding of the SSS will be described.

A sequence used for the SSS is configured by interleaving two length-31m-sequences and combining the two sequences, and it transmits 168 cellgroup IDs. The m-sequence used as the sequence of the SSS is robust in afrequency selective environment and a computational load may be reducedby fast m-sequence transformation using Fast Hadamard Transform. Inaddition, configuration of the SSS using two short codes is proposed inorder to reduce the computational load of the UE.

FIG. 4 is a diagram showing two sequences in a logical regioninterleaved and mapped in a physical region.

When the two m-sequences used to generate the SSS code are respectivelydefined as S1 and S2, if the SSS of subframe 0 transmits a cell group IDusing a combination of (S1, S2), the SSS of subframe 5 transmits a cellgroup ID after swapping (S1, S2) with (S2, S1), thereby identifying a10-ms frame boundary. At this time, the used SSS code uses a polynomialof x⁵+x²+1 and a total of 31 codes may be generated via differentcircular shifts.

In order to enhance reception performance, two different PSS-basedsequences may be defined and scrambled with the SSS and differentsequences are scrambled with S1 and S2. Thereafter, an S1-basedscrambling code is defined to perform scrambling with S2. At this time,the code of the SSS is swapped in units of 5 ms, but the PSS-basedscrambling code is not swapped. The PSS-based scrambling code is definedin six cyclic shift versions according to the PSS index in them-sequence generated from the polynomial of x⁵+x³+1 and the S1-basedscrambling code is defined in eight cyclic shift versions according tothe index of S1 in the m-sequence generated from the polynomial ofx⁵+x⁴+x²+x¹+1.

Cell search in NB-IoT or NB-LTE which is a model obtained by applyingNB-IoT to an LTE system is the same as the above-described LTE system. Aused sequence needs to be modified according to NB-LTE properties and,hereinafter, portions to be modified as compared to the LTE system willbe focused upon.

FIG. 5 is a diagram showing the overall structure in whichsynchronization signals are transmitted and received in an NB LTEsystem.

As shown in FIG. 5, even in the NB-LTE system, a PSS and an SSS aredivided and transmitted and are respectively referred to as NB-PSS andNB-SSS in order to be distinguished from the legacy PSS and SSS.However, a PSS and an SSS may be used if such use will not lead toconfusion.

Even in the NB-LTE system, similarly to the legacy LTE system, 504 NBcell identities through a synchronization channel need to be indicated.In the NB-LTE system according to the embodiment of the presentinvention, the NB-PSS is transmitted using one specific sequence.Therefore, the 504 NB cell identities need to be indicated using theNB-SSS only.

In a receiving device, auto-correlation is generally performed to detectthe PSS. To this end, the receiving device attempts to detect the PSSusing a sliding window method in the time domain. The method ofdetecting the PSS may increase complexity of the receiving device andthus may not be suitable for the NB-LTE system for decreasingcomplexity. Since the NB-PSS according to the present embodiment istransmitted using one specific sequence, the receiving device mayperform only operation for detecting the specific sequence, therebyreducing complexity. For example, if a Zadoff-Chu (ZC) sequence is usedfor the NB-PSS, the root index of this ZC sequence may be fixed to onepredetermined value (e.g., u=5). Since the NB-PSS is simply configured,the NB-SSS needs to be used to efficiently indicate the 504 cellidentities, which will be described below as another aspect of thepresent invention.

In one embodiment of the present invention, the NB-PSS may be repeatedlytransmitted in a plurality of OFDM symbols. Although the NB-PSS isrepeatedly transmitted in nine OFDM symbols in the example of FIG. 5,the number of OFDM symbols is not limited thereto. Since one subframeusing an extended CP may include 12 OFDM symbols and the first threeOFDM symbols of the 12 OFDM symbols may be used to transmit a PDCCH, theNB-PSS is repeatedly transmitted in the nine OFDM symbols in the exampleof FIG. 5. The above-described numerical values may be changed accordingto change in the number of OFDM symbols included in one subframe of theNB-LTE system and a maximum number of OFDM symbols required to transmitthe PDCCH. For example, if the number of OFDM symbols included in onesubframe is 14 and a maximum number of OFDM symbols used to transmit aPDCCH is 3, the number of OFDM symbols in which the NB-PSS is repeatedlytransmitted may be 11. In the present embodiment, the NB-PSS may berepeatedly transmitted in a plurality of OFDM symbols which iscontinuously arranged in the time domain.

If the NB-PSS corresponds to resource elements for transmitting a CRS inan LTE system for providing an NB-LTE service upon mapping to resourceelements in the time-frequency domain, the NB-PSS element may bepunctured to prevent collision. That is, the transmission position ofthe NB-PSS/NB-SSS may be designed to avoid collision with legacy LTEsignals such as a PDCCH, a PCFICH, a PHICH and an MBSFN.

As the NB-PSS is repeatedly transmitted in the plurality of OFDMsymbols, the receiving device may easily determine a subframe timing anda frequency offset.

Even the NB-SSS may be transmitted over a plurality of OFDM symbols asshown in FIG. 5. As described above, since the NB-SSS is used toindicate the cell identities, a method of generating a long sequence anddividing and transmitting the long sequence in a plurality of OFDMsymbols is proposed. Although the NB-SSS is transmitted over six OFDMsymbols in FIG. 5, the number of OFDM symbols in which the NB-SSS istransmitted is not limited thereto. For example, the NB-SSS may betransmitted over 11 OFDM symbols similarly to the above-describedNB-PSS.

As described above, NB-IoT has system bandwidth corresponding to 1 PRBin an LTE system and supports low complexity and low power consumption.To this end, this may be mainly used as a communication system forimplementing IoT by supporting a machine-type communication (MTC)apparatus in a cellular system. By using the same OFDM parameters, suchas subcarrier spacing as in legacy LTE, one PRB for NB-IoT may beallocated to a legacy LTE band without allocating an additional band,such that the frequency is efficiently used.

Hereinafter, the method of transmitting the NB-PSS and the NB-SSS willbe described in detail based on the above description.

NB-PSS Transmission

FIG. 6 is a diagram illustrating a method of repeatedly transmitting anNB-PSS in a plurality of OFDM symbols according to an embodiment of thepresent invention.

As described above, the NB-PSS is transmitted using a plurality of OFDMsymbols. At this time, the same sequence is repeatedly transmitted inthe OFDM symbols and each OFDM symbol is multiplied by a specific coversequence as shown in FIG. 6.

On the assumption of system bandwidth of 1 PRB and subcarrier spacing of15 KHz, a maximum length of a sequence which may be transmitted in oneOFDM symbol is 12. For convenience of description, hereinafter, assumethat the system bandwidth of the NB-LTE system is 1 PRB and thesubcarrier spacing is 15 KHz.

The PSS is generally detected in the receiving device in the time domainin consideration of computational complexity. In the PSS, in order toacquire time/frequency synchronization, a sliding window is applied to aPSS sequence to perform correlation. In the PSS transmission structureshown in FIG. 6, since the same sequence is transmitted in every OFDMsymbol, a relatively large correlation value can be obtained in a periodcorresponding to the length of an OFDM symbol. When the condition of acomplementary Golay sequence is used, the period for outputting therelatively large correlation value may be increased to improvecorrelation properties.

In addition, by applying a cover sequence to every OFDM symbol as shownin FIG. 6, it is possible to further improve correlation properties. Atthis time, a method of transmitting a PSS using a complementary Golaysequence is as follows.

Method 1: Method of alternately arranging a pair of complementary Golaysequences in OFDM symbols.

For example, on the assumption of N=6 OFDM symbols, a(n) is transmittedin OFDM symbol 1 and b(n) is transmitted in OFDM symbol 2. At this time,c(n) is applicable by taking length 6 of an m-sequence of length 7. Atthis time, the number of OFDM symbols for transmitting the PSS ispreferably an even number. If it is assumed that complementary Golaysequences are binary sequences, a possible sequence length is2^(a)10^(b)26^(c) (a, b and c being an integer equal to or greater than0.). If only 12 available resources are present in one OFDM symbol, thepossible Golay sequence length may be 10. One embodiment of a pair oflength-10 complement Golay sequences is a(n)=[1 1−1 −1 1 1 1−1 1−1],b(n)=[1 1 1 1 1−1 1−1 −1 1]. REs, to which the sequence is notallocated, of the OFDM symbols are filled with 0 and are transmitted. Ifa non-binary complementary Golay sequence is assumed, since a sequencepair is present without length limit, a pair of length-12 sequences a(n)and b(n) may be transmitted in the OFDM symbols using the same method.

FIG. 7 is a diagram showing correlation properties of a pair oflength-10 complementary sequences a(n) and b(n) and various c(n)patterns.

As another method, if the PSS is transmitted in an odd number of OFDMsymbols, the PSS may be transmitted such that one of the pair ofsequences is transmitted once more. For example, in the case of N=7 OFDMsymbols, a(n), b(n), a(n), b(n), a(n), b(n) and a(n) may be transmittedin the OFDM symbols in this order.

Method 2: Method of arranging a pair of complementary Golay sequences inone OFDM symbol.

Method 2-1: Method of generating and arranging a sequence correspondingto ½ of one OFDM symbol.

For example, on the assumption of N=6 OFDM symbols, length-6 non-binarycomplementary Golay sequences a(n) and b(n) are generated, a(n) isallocated to and transmitted in ½ of available REs of one OFDM symboland b(n) is allocated to and transmitted in the remaining ½ of theavailable REs. At this time, in RE allocation, a(n) may be allocated tothe first half and b(n) may be allocated to the second half.

Method 2-2: Method of superpositioning and transmitting a(n) and b(n) inone OFDM symbol.

For example, on the assumption of N=6 OFDM symbols, length-10/12binary/non-binary complementary Golay sequences may be generated anda(n)+b(n) may be computed and transmitted.

Method 3: Method of arranging and transmitting L (L>2) or morecomplementary Golay sequences.

At this time, the number of OFDM symbols for transmitting the PSS shouldsatisfy the multiple conditions of L. For example, when L=3 and N=6, thelength-10 or length-12 complementary Golay sequences la(n), lb(n) andlc(n) may be sequentially arranged and transmitted in the OFDM symbols.That is, the sequences are arranged in order of la(n), lb(n), lc(n),la(n), lb(n) and lc(n) and are transmitted after applying a coversequence c(n).

Meanwhile, in the above-described NB-PSS transmission method, a ZCsequence having elements corresponding in number to 12 subcarriers maybe used in the frequency domain of one OFDM symbol. In order to preventthe NB-PSS from being mapped to a DC element, only 11 subcarriers may beused and thus a length-11 ZC sequence may be used.

As a detailed example of the above-described NB-PSS transmission method,the sequence d₁(n) of the NB-PSS may be generated using the length-11 ZCsequence in the frequency domain as follows.

$\begin{matrix}{{{d_{l}(n)} = {{S(l)} \cdot e^{{- j}\frac{\pi\;{{un}{({n + 1})}}}{11}}}},{n = 0},1,\ldots\mspace{14mu},10} & {{Equation}\mspace{14mu} 3}\end{matrix}$

where, the root index (u) of the ZC sequence may be specified to aspecific root index as described above. In the present embodiment,assume that u=5, without being limited thereto.

In Equation 3, s(1) denotes the above-described cover sequence and S(1)may be defined according to the OFDM symbol index “1” as follows.

TABLE 1 Cyclic prefix length S(3), . . . , S(13) Normal 1 1 1 1 −1 −1 11 1 −1 1

NB-SSS Transmission

As described above with regard to embodiments of the present invention,since the NB-PSS is transmitted using one specific sequence, 504 NB cellidentities are indicated. Therefore, a method of transmitting the NB-SSSthrough a plurality of OFDM symbols similarly to the NB-PSS anddivisionally mapping a long sequence to the plurality of OFDM symbols inorder to indicate the cell identities is proposed.

FIG. 8 is a diagram illustrating the concept of transmitting an NB-SSSaccording to an embodiment of the present invention.

By detecting an SSS, a receiving device, that is, UE, may acquireinformation on cell id detection, a subframe index for transmission ofthe SSS and the other system information. In the transmission structureof the SSS, a sequence may not be repeatedly transmitted in a pluralityof OFDM symbols similarly to the PSS, but a long length-M sequence isdivisionally transmitted in a plurality of OFDM symbols.

In FIG. 8, a length-M sequence may be generated and multiplied by alength-M scrambling sequence in element units. The length-M sequence maybe divided into length-L (M>=L) sequences, and the length-L sequencesmay be respectively arranged in N OFDM symbols, multiplied by ascrambling sequence s(n), and transmitted in the N OFDM symbols. Forexample, on the assumption of M=72, L=12 and N=6, the length-72 sequenceis divided into 6 length-12 sequences and the length-12 sequences arerespectively transmitted in six OFDM symbols. The above-describednumerical values are exemplary and the numerical values may be changedas long as M=L*N is satisfied.

At this time, a method of designing an SSS sequence in order to transmitinformation is as follows.

In legacy LTE, 504 physical cell IDs are indicated by a PSS and an SSS.In contrast, in NB-IoT, an NB-SSS indicates 504 physical cell IDs. Inlegacy LTE, a PBCH is transmitted at a period of 10 ms and a PSS/SSS istransmitted at a period of 5 ms. Therefore, since the PSS/SSS istransmitted twice during the transmission period of the PBCH, the numberof an SSS transmission subframe is indicated through the SSS, and SSS1and SSS2 configuring the SSS are swapped according to subframe position,thereby indicating the subframe index. In NB-IoT, an NB-PBCH istransmitted at a period of 80 ms, an NB-PSS is transmitted at a periodof 10 ms, and an NB-SSS is transmitted at a period greater than that ofthe NB-PSS (e.g., 20 ms or 40 ms). If the transmission period of theNB-SSS is less than that of the NB-PBCH transmission period of 80 ms,the number of candidate positions where the NB-SSS may be transmitted inthe NB-PBCH transmission period may be increased as compared to LTE.

In summary, the NB-SSS should include a significantly large amount ofinformation such as a cell-ID and an NB-SSS frame index. There is a needto design an NB-SSS capable of simplifying reception complexity of a UEwhile including a large amount of information.

To this end, in one embodiment of the present invention, in addition tothe method of divisionally transmitting a long sequence in a pluralityof OFDM symbols as described with reference to FIG. 8, a configurationof an NB-SSS is divided into several sequences. More specifically, theNB-SSS may be configured by a combination of a base-sequence, ascrambling sequence, a cyclic shift and a cover sequence. For example,an L-length ZC sequence is generated as the base-sequence, iselement-wise multiplied by an L-length scrambling sequence, is subjectedto cyclic shift and is element-wise multiplied by an L-length coversequence.

FIG. 9 is a diagram illustrating a method of generating and transmittingan NB-SSS according to an embodiment of the present invention.

In FIG. 9, first, a length-M ZC sequence may be generated.S _(ZC)(u,n)=exp(jΠun(n+1)/L), where u: root index, n: sequenceindex  Equation 4

Assume that this ZC sequence is long enough to divisionally transmit theNB-SSS in a plurality of OFDM symbols as described above. In the presentembodiment, M=132 (12 subcarriers*11 OFDM symbols). Here, 11 OFDMsymbols may be obtained by subtracting three OFDM symbols, in which aPDCCH may be transmitted, from 14 OFDM symbols included in one subframe,as in the above description of the NB-PSS. The number of OFDM symbolsmay be changed according to system implementation.

In a ZC sequence, root indices may be identified when the length of asequence is a prime number. Therefore, as described above, rather than alength-132 ZC sequence, 131 which is the largest prime number less than132 may be used as the length of the ZC sequence. The length-131 ZCsequence may be cyclically extended to a length-132 ZC sequence asfollows.S _(ZC)(u,n)=exp(jΠun′(n′+1)/M),  Equation 5

where u: root index

n=0, 1, . . . , M

n′=n mod M

As described above, in an NB-LTE system, since one specific sequence isused as an NB-PSS, 504 cell IDs need to be identified by the NB-SSS andthus the length-131 ZC sequence is insufficient to indicate 504 cellIDs. To this end, in one embodiment of the present invention, as shownin FIG. 9, the ZC sequence is multiplied by a length-M cover sequence inelement units and this cover sequence indicates a predetermined numberof offsets or position indices, such that the resultant NB-SSS indicatesall cell IDs. For example, at least four offsets are required toindicate 504 cell IDs. Accordingly, in one embodiment of the presentinvention, the number of root indices of the ZC sequence is 126 lessthan the length of M (131) and 126*4=504 cell IDs may be indicatedthrough cover sequence, by which the ZC sequence is multiplied inelement units.

In FIG. 9, indication of the position of the NB-SSS using the length-Mcover sequence is shown. As described above, the NB-SSS may betransmitted less frequently than the NB-PSS and thus signaling thereofmay be required. As a method of transmitting, through the NB-SSS,information on the position where the NB-SSS is transmitted, a method ofapplying a cyclic shift to the ZC sequence as described above may beused in addition to the method of transmitting the information on theposition of the NB-SSS through the cover sequence. In some cases, theabove-described offset is applicable to the ZC sequence instead of thecover sequence.

As described above, 131 root indices may be selected in the length-131ZC sequence. However, if four offsets are used to indicate 504 cell IDs,since only 126 root indices are selected from among 131 root indices,root indices having good performance among the 131 root indices may beused.

FIG. 10 is a diagram illustrating a method of selecting root indices ofa ZC sequence to be used in an NB-SSS according to an embodiment of thepresent invention.

If a long single ZC sequence is used upon configuring an NB-SSS, a PAPRmay be increased although the ZC sequence is used. The NB-SSS has a PAPRchanged according to root index. In particular, low root indices (highroot indices paired therewith) and middle root indices may generate ahigh PAPR.

A variety of combinations capable of expressing 504 PCIDs may beconsidered. For example, 126 root indices×4 additional indices, 84 rootindices×6 additional indices, 42 root indices×12 additional indices,etc. may be considered.

In a length-131 ZC sequence, root indices 1, 130, 2, 129, 3, 128, 65,66, 64, 67, etc. generate high PAPRs. (a) of FIG. 10 shows the casewhere root indices indicating high PAPRs are used and (b) of FIG. 10shows the case where root indices indicating low PAPRs are used.

If 126 root indices are used, four root indices are excluded from rootindices 1 to 130. Therefore, in one embodiment of the present invention,root indices which generate high PAPRs may be excluded and indices 3 to128 are used. In this case, an average PAPR may be decreased. That is,in the present embodiment, the root indices of a length-L ZC sequenceused to transmit the NB-SSS are selected from among M root indices (Mbeing less than L) and the M root indices are not selected from a rangeof [0, M−1] but are selected from [k, MA−1] using a predeterminedoffset. Preferably, the ZC sequence is selected from among 126 rootindices in a range of [3, 128].

The above description will be summarized as follows.

In an NB-LTE system, an NB-SSS may be transmitted at a period of 20 ms.

This NB-SSS may indicate 504 PCIDs and may indicate the transmissionpositions of the 504 PCIDs in a range of 80 ms.

In addition, the NB-SSS sequence is generated using a length-131 ZCsequence in the frequency domain. At this time, root indices may beselected in a range of [3, 128]. This ZC sequence may be subjected tocyclic shift and then multiplied by a binary scrambling sequence inelement units. In such a structure, 504 PCIDs may be represented by 126ZC root indices and four binary scrambling sequences. In addition, theposition of the NB-SSS in the range of 80 ms may be represented by fourcyclic shift values (e.g., 0, 33, 66 and 99).

The binary scrambling sequences used as the cover sequence may be thefollowing Hadamard sequences.b _(q)(n)=Hadamard_(2q-1) ^(128×128)(mod(n,128)),q=0,1,2,3  Equation 6

Using this, the NB-SSS may be configured as follows.

$\begin{matrix}{{{SSSu},q,{{k(n)} = {{S_{u}(n)}*{{bq}(n)}*{{Ck}(n)}}}}{{{{Su}(n)} = {\exp\left( {j\;{\pi\left( {u + 3} \right)}{{n\left( {n + 1} \right)}/131}} \right)}},{n = 0},\ldots\mspace{14mu},131,{u = 0},\ldots\mspace{14mu},{{125{b_{q}(n)}} = {{Hadamard}_{2^{q} - 1}^{128 \times 128}\left( {{mod}\left( {n,128} \right)} \right)}},{q = 0},1,2,3,{n = 0},\ldots\mspace{14mu},131,{q = 0},1,2,{{3{C_{k}(n)}} = {\exp\left( {{- j}\; 2\;\pi\; 33\;{{kn}/132}} \right)}},{n = 0},\ldots\mspace{14mu},131,{k = 0},1,2,3}{q = \left\lfloor {{PCID}/126} \right\rfloor}{{u = {{mod}\left( {{PCID},126} \right)}},{k = {{Subframe}\mspace{14mu}{indication}}}}} & {{Equation}\mspace{14mu} 7}\end{matrix}$

Hereinafter, a Hadamard sequence used in the above-described structurewill be described.

FIG. 11 is a diagram showing a cross correlation value when a specificHadamard sequence is used in an NB-SSS in one embodiment of the presentinvention.

As shown in FIG. 11, a sequence having the same time-domain cyclic shiftas the Hadamard sequence (e.g., [1 1 1 1 . . . ], [1−1 1−1 . . . ]) mayhave poor cross-correlation properties.

In order to solve such a problem, in one embodiment of the presentinvention, when four sequences selected from the Hadamard sequences areused, sequences which are not included in a time-domain cyclic shift areused. For example, if [1 1 1 1 . . . ], [1−1 1−1 . . . ], etc. areincluded in the time-domain cyclic shift, 1 and 2 are sequences composedof [1 1 1 1 . . . ], [1−1 1−1 . . . ] in a Hadamard matrix and thus areexcluded. In this case, upon q=0, 1, 2, 3, N (>=4) times of q may beselected.

$\begin{matrix}{{{SSSu},q,{{k(n)} = {{S_{u}(n)}*{{bq}(n)}*{{Ck}(n)}}}}{{{{Su}(n)} = {\exp\left( {j\;\pi\;\left( {u + 3} \right){{n\left( {n + 1} \right)}/131}} \right)}},{n = 0},\ldots\mspace{14mu},131,{u = 0},\ldots\mspace{14mu},125}{{{b_{q}(n)} = {{Hadamard}_{2^{q} - 1}^{128 \times 128}\left( {{mod}\left( {n,128} \right)} \right)}},{n = 0},\ldots\mspace{14mu},131,{q = 0},1,2,{{3{C_{k}(n)}} = {\exp\left( {{- j}\; 2\pi\; 33\;{{kn}/132}} \right)}},{n = 0},\ldots\mspace{14mu},131,{k = 0},1,2,{{3u} = {{mod}\left( {{PCID},126} \right)}},{q = \left\lfloor {{PCID}/126} \right\rfloor},{k = {{Subframe}\mspace{14mu}{indication}}}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

In another embodiment of the present invention, the Hadamard sequence isbinary. If a time-domain cyclic shift is composed of a complex value,since a sequence of a domain different from that of the Hadamardsequence is generated, ambiguity between the two sequences is removed.For example, if a time-domain cyclic shift is composed of offsetsdifferent in number from 33 offsets in 132 samples, the sequence mayinclude a sequence having a complex value. Time-domain shift valuesmaintaining an equal distance possible in a length-132 sequence are 32,34, etc. In addition, 36 offsets may be assumed.

If the Hadamard sequence and the time-domain cyclic shift are configuredin different domains, a full orthogonal sequence or a quasi-orthogonalsequence is applicable as the Hadamard sequence.

If a 128-Hadamard matrix is cyclically extended to 132, sequences ofq=0, 1, 2 and 3 are fully orthogonal to one another.

The following equations are examples of the embodiments. In addition tothe following examples, there are various examples satisfying theabove-described principle.

$\begin{matrix}{{{SSSu},q,{{k(n)} = {{{Su}(n)}*{{bq}(n)}*{{Ck}(n)}}}}{{{{Su}(n)} = e^{j\frac{{\pi{({u + 3})}}{n{({n + 1})}}}{131}}},{n = 0},\ldots\mspace{14mu},131,{u = 0},\ldots\mspace{14mu},125}{{{{bq}(n)} = {{Hadamard}_{q}^{128 \times 128}\left( {{mod}\left( {n,128} \right)} \right)}},{n = 0},\ldots\mspace{14mu},131,{q = 0},1,2,3}{{{C_{k}(n)} = e^{{- j}\frac{2\pi\; 32\;{kn}}{132}}},{n = 0},\ldots\mspace{14mu},131,{k = 0},1,2,3}{{u = {{mod}\left( {{PCID},126} \right)}},{q = \left\lfloor \frac{PCID}{126} \right\rfloor},{k = {{Subframe}\mspace{14mu}{indication}}}}} & {{Equation}\mspace{14mu} 9} \\{{{SSSu},q,{{k(n)} = {{{Su}(n)}*{{bq}(n)}*{{Ck}(n)}}}}{{{{Su}(n)} = e^{j\frac{{\pi{({u + 3})}}{n{({n + 1})}}}{131}}},{n = 0},\ldots\mspace{14mu},131,{u = 0},\ldots\mspace{14mu},125}{{{{bq}(n)} = {{Hadamard}_{2^{q} - 1}^{128 \times 128}\left( {{mod}\left( {n,128} \right)} \right)}},{n = 0},\ldots\mspace{14mu},131,{q = 0},1,2,3}{{{C_{k}(n)} = e^{{- j}\frac{2\pi\; 32\;{kn}}{132}}},{n = 0},\ldots\mspace{14mu},131,{k = 0},1,2,3}{{u = {{mod}\left( {{PCID},126} \right)}},{q = \left\lfloor \frac{PCID}{126} \right\rfloor},{k = {{Subframe}\mspace{14mu}{indication}}}}} & {{Equation}\mspace{14mu} 10} \\{{{SSu},q,{{k(n)} = {{{Su}(n)}*{{bq}(n)}*{{Ck}(n)}}}}{{{{Su}(n)} = e^{j\frac{{\pi{({u + 3})}}{n{({n + 1})}}}{131}}},{n = 0},\ldots\mspace{14mu},131,{u = 0},\ldots\mspace{14mu},125}{{{{bq}(n)} = {{Hadamard}_{2^{q} - 1}^{128 \times 128}\left( {{mod}\left( {n,128} \right)} \right)}},{n = 0},\ldots\mspace{14mu},131,{q = 0},1,2,3}{{{C_{k}(n)} =},{n = 0},\ldots\mspace{14mu},131,{k = 0},1,2,3}{{u = {{mod}\left( {{PCID},126} \right)}},{q = \left\lfloor \frac{PCID}{126} \right\rfloor},{k = {{Subframe}\mspace{14mu}{indication}}}}} & {{Equation}\mspace{14mu} 11} \\{{{SSu},q,{{k(n)} = {{{Su}(n)}*{{bq}(n)}*{{Ck}(n)}}}}{{{{Su}(n)} = e^{j\frac{{\pi{({u + 3})}}{n{({n + 1})}}}{131}}},{n = 0},\ldots\mspace{14mu},131,{u = 0},\ldots\mspace{14mu},125}{{{{bq}(n)} = {{Hadamard}_{q}^{128 \times 128}\left( {{mod}\left( {n,128} \right)} \right)}},{n = 0},\ldots\mspace{14mu},131,{q = 0},1,2,3}{{{C_{k}(n)} =},{n = 0},\ldots\mspace{14mu},131,{k = 0},1,2,3}{{u = {{mod}\left( {{PCID},126} \right)}},{q = \left\lfloor \frac{PCID}{126} \right\rfloor},{k = {{Subframe}\mspace{14mu}{indication}}}}} & {{Equation}\mspace{14mu} 12} \\{{{SSu},q,{{k(n)} = {{{Su}(n)}*{{bq}(n)}*{{Ck}(n)}}}}{{{{Su}(n)} = e^{j\frac{{\pi{({u + 3})}}{n{({n + 1})}}}{131}}},{n = 0},\ldots\mspace{14mu},131,{u = 0},\ldots\mspace{14mu},125}{{{{bq}(n)} = {{Hadamard}_{2^{q}}^{128 \times 128}\left( {{mod}\left( {n,128} \right)} \right)}},{n = 0},\ldots\mspace{14mu},131,{q = 0},1,2,3}{{{C_{k}(n)} =},{n = 0},\ldots\mspace{14mu},131,{k = 0},1,2,3}{{u = {{mod}\left( {{PCID},126} \right)}},{q = \left\lfloor \frac{PCID}{126} \right\rfloor},{k = {{Subframe}\mspace{14mu}{indication}}}}} & {{Equation}\mspace{14mu} 13}\end{matrix}$

Equation 14 below shows an NB-SSS (d(n)) according to another embodimentof the present invention, which shows a sequence for a cyclic shift anda Hadamard sequence.

$\begin{matrix}{{{d(n)} = {{b_{q}(m)}e^{{- {j2}}\;\pi\;\theta_{f}n}e^{{- j}\frac{\pi\;{{un}^{\prime}{({n^{\prime} + 1})}}}{131}}}}{{n = 0},1,\ldots\mspace{14mu},131}{n^{\prime} = {n\;{mod}\; 131}}{m = {n\;{mod}\; 128}}{u = {{N_{ID}^{Ncell}{mod}\; 126} + 3}}{{where},{q = \left\lfloor \frac{N_{ID}^{Ncell}}{126} \right\rfloor}}} & {{Equation}\mspace{14mu} 14}\end{matrix}$

Meanwhile, in Equation 14 above, a binary sequence b_(q)(m) may be givenas shown in the following table.

TABLE 2 q b_(q) (0), . . . , b_(q) (127) 0 [1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1] 1 [1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 1 −1−1 1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 −1 1 1−1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1−1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1−1 −1 1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1] 2 [1 −1 −1 1 −1 1 1 −1−1 1 1 −1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1−1 −1 1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 1 −1−1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1−1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −11 −1 −1 1] 3 [1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 1 −1 −11 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1−1 1 1 −1 −1 1 1 −1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 1−1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1−1 1 −1 1 1 −1 1 −1 −1 1 1 −1 −1 1 −1 1 1 −1]

Meanwhile, in Equation 14 above, a cyclic shift value θ_(f) in a framenumber n_(f) may be determined as follows.

$\begin{matrix}{\theta_{f} = {\frac{33}{132}\left( {n_{f}/2} \right){mod}\; 4}} & {{Equation}\mspace{14mu} 15}\end{matrix}$

Resource Structure

A resource structure in a system, to which an NB-PSS and an NB-SSS areapplicable will now be described.

FIG. 12 is a diagram showing an example of a downlink (DL)/uplink (UL)slot structure in a wireless communication system.

Referring to FIG. 12, a slot includes a plurality of orthogonalfrequency division multiplexing (OFDM) symbols in the time domain andincludes a plurality of resource blocks (RBs) in the frequency domain.The OFDM symbol means one symbol interval. Referring to FIG. 12, asignal transmitted in each slot may be represented by a resource gridcomposed of N^(DL/UL) _(RB)×N^(RB) _(sc) subcarriers and N^(DL/UL)_(symb) OFDM symbols. Here, N^(DL) _(RB) indicates the number ofresource blocks (RBs) in a DL slot and N^(UL) _(RB) indicates the numberof RBs in a UL slot. N^(DL) _(RB) and N^(UL) _(RB) depend on DLtransmission bandwidth and UL transmission bandwidth, respectively.N^(DL) _(symb) denotes the number of OFDM symbols in a DL slot andN^(UL) _(symb) denotes the number of OFDM symbols in a UL slot. N^(RB)_(sc) denotes the number of subcarriers configuring one RB.

The OFDM symbol may be referred to as an OFDM symbol, a single carrierfrequency division multiplexing (SC-FDM) symbol, etc. according tomultiple access method. The number of OFDM symbols included in one slotmay be variously changed according to length of a cyclic prefix (CP).For example, one slot includes seven OFDM symbols in the case of anormal CP and includes six OFDM symbols in the case of an extended CP.Although, for convenience of description, one slot of a subframeincludes 7 OFDM symbols in FIG. 12, the embodiments of the presentinvention are applicable to subframes having different numbers of OFDMsymbols.

Referring to FIG. 12, each OFDM symbol includes N^(DL/UL) _(RB)×N^(RB)_(sc) subcarriers in the frequency domain. The type of the subcarriermay be divided into a data subcarrier for data transmission, a referencesignal subcarrier for transmission of a reference signal and a nullsubcarrier for a guard band or a direct current (DC) element. The DCelement is mapped to a carrier frequency _(ƒ0) in an OFDM signalgeneration process or a frequency up-conversion process. A carrierfrequency is also referred to as a center frequency _(ƒc).

One RB is defined as N^(DL/UL) _(symb) (e.g., 7) consecutive OFDMsymbols in the time domain and N^(RB) _(sc) (e.g., 1) consecutivesubcarriers in the frequency domain. For reference, a resource composedof one OFDM symbol and one subcarrier is referred to as a resourceelement (RE) or tone. Accordingly, one RB is composed of N^(DL/UL)_(symb)×N^(RB) _(sc) REs. Each RE in the resource grid may be uniquelydefined by an index pair (k, l) in one slot. k indicates an index from 0to N^(DL/UL) _(RB)×N^(RB) _(sc)−1 in the frequency domain and lindicates an index from 0 to N^(DL/UL) _(symb)−1 in the time domain.

Meanwhile, one RB is mapped to one physical resource block (PRB) and onevirtual resource block (VRB). The PRB is defined by N^(DL/UL) _(symb)(e.g., 7) consecutive OFDM symbols or SC-FDM symbols in the time domainand is defined by N^(RB) _(sc) (e.g., 12) consecutive subcarriers in thefrequency domain. Accordingly, one PRB is composed of N^(DL/UL)_(symb)×N^(RB) _(sc) REs. Two RBs respectively located in two slots ofthe subframe while occupying the same N^(RB) _(sc) consecutivesubcarriers in one subframe are referred to as a PRB pair. Two RBsconfiguring the PRB pair have the same PRB number (or PRB index).

FIG. 13 is a diagram showing a downlink subframe structure used in awireless communication system.

Referring to FIG. 13, a DL subframe is divided into a control region anda data region in the time domain. Referring to FIG. 13, a maximum ofthree (four) OFDM symbols of a front portion of a first slot within asubframe corresponds to a control region to which a control channel isallocated. Hereinafter, a resource region available for PDCCHtransmission in a DL subframe is referred to as a PDCCH region. Theremaining OFDM symbols other than the OFDM symbol(s) used in the controlregion correspond to a data region to which a Physical Downlink SharedChannel (PDSCH) is allocated. Hereinafter, a resource region availablefor PDSCH transmission in a DL subframe is referred to as a PDSCHregion. Examples of the downlink control channels include, for example,a Physical Control Format Indicator Channel (PCFICH), a PhysicalDownlink Control Channel (PDCCH), a Physical Hybrid automatic repeatrequest Indicator Channel (PHICH), etc. The PCFICH is transmitted at afirst OFDM symbol of a subframe, and carries information about thenumber of OFDM symbols used to transmit the control channel within thesubframe. The PHICH carries a hybrid automatic repeat request (HARQ)acknowledgement (ACK)/negative-acknowledgement (NACK) signal in responseto uplink transmission.

The control information transmitted through the PDCCH is referred to asDownlink Control Information (DCI). The DCI includes resource allocationinformation and other control information for a UE or UE group. Transmitformat and resource allocation information of a DL shared channel(DL-SCH) is also referred to as DL scheduling information or DL grantand transmit format and resource allocation information of a UL-SCH isalso referred to as UL scheduling information or UL grant. The size andusage of the DCI carried by one PDCCH are changed according to DCIformat and the size of the DCI may be changed according to coding rate.In the current 3GPP LTE system, formats 0 and 4 are defined for uplinkand various formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3, 3A, etc. aredefined for downlink. According to usage of the DCI format, anycombination of control information such as hopping flag, RB allocation,modulation and coding scheme (MCS), redundancy version (RV), new dataindicator (NDI), transmit power control (TPC), cyclic shift demodulationreference signal (DM RS), UL index, channel quality information (CQI)request, DL assignment index, HARQ process number, transmitted precodingmatrix indicator (TPMI), precoding matrix indicator (PMI), etc. istransmitted to a UE as downlink control information.

A plurality of PDCCHs may be transmitted in the control region. The UEmay monitor the plurality of PDCCHs. An eNB determines a DCI formataccording to DCI to be transmitted to a UE and attaches cyclicredundancy check (CRC) to the DCI. The CRC is masked (scrambled) with aRadio Network Temporary Identifier (RNTI) according to an owner or usageof the PDCCH. For example, if the PDCCH is for a specific UE, acell-RNTI (C-RNTI) of the UE may be masked to the CRC. Alternatively, ifthe PDCCH is for a paging message, a paging radio network temporaryidentifier (P-RNTI) may be masked to the CRC. If the PDCCH is for systeminformation (more specifically, a system information block (SIB)), asystem information RNTI (SI-RNTI) may be masked to the CRC. If the PDCCHis for random access response, a random access-RNTI (RA-RNTI) may bemasked to the CRC. CRC masking (or scrambling) includes XOR operation ofCRC and RNTI at a bit level, for example.

The PDCCHs are transmitted as an aggregate of one or several consecutivecontrol channel elements (CCEs). The CCE is a logical allocation unitused to provide the PDCCHs with a coding rate based on the state of aradio channel. The CCE corresponds to a plurality of resource elementgroups (REGs). For example, one CCE corresponds to 9 REGs and one REGcorresponds to four REs. Four QPSKs symbols are mapped to respectiveREGs. The RE occupied by the RS is not included in the REG. Accordingly,the number of REGs within a given OFDM symbol is changed depending onwhether an RS is present. The concept of the REG is used even in otherdownlink control channels (that is, PCFICH and PHICH). The DCI formatand the number of DCI bits are determined according to the number ofCCEs. The CCEs are numbered and consecutively used and, in order tosimplify a decoding process, a PDCCH having a format composed of n CCEsmay start at only a CCE having a number corresponding to a multiple ofn. The number of CCEs used for transmission of a specific PDCCH isdetermined according to channel state or by a network or an eNB. Forexample, in the case of a PDCCH for a UE having a good DL channel (e.g.,adjacent to an eNB), only one CCE may be used. However, in the case of aPDCCH for a UE having a poor channel state (e.g., located near a celledge), 8 CCEs may be required in order to obtain sufficient robustness.In addition, the power level of the PDCCH may be controlled according tochannel state.

Apparatus Configuration

FIG. 14 is a block diagram showing the components of a transmittingdevice 10 and a receiving device 20 for performing embodiments of thepresent invention.

The transmitting device 10 and the receiving device 20 include radiofrequency (RF) units 13 and 23 for transmitting or receiving a radiosignal carrying information and/or data, a signal and a message,memories 12 and 22 for storing a variety of information associated withcommunication in a wireless communication system, and processors 11 and21 operatively connected to the components including the RF units 13 and23 and the memories 12 and 22 and configured to control the memories 12and 22 and/or the RF units 13 and 23 to perform at least one of theembodiments of the present invention, respectively.

The memories 12 and 22 may store programs for processing and controllingthe processors 11 and 21 and may temporarily store input/output signal.The memories 12 and 22 may be used as a buffer.

The processors 11 and 21 generally control the overall operation of thevarious modules of the transmitting device and the receiving device. Inparticular, the processors 11 and 21 may perform a variety of controlfunctions for performing the present invention. The processors 11 and 21may be referred to as a controller, a microcontroller, a microprocessor,a microcomputer, etc. The processors 11 and 21 can be implemented by avariety of means, for example, hardware, firmware, software, or acombination thereof. In the case of implementing embodiments of thepresent invention by hardware, application specific integrated circuits(ASICs), Digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), etc. configured to perform embodiments of thepresent invention may be included in the processors 11 and 21. Ifoperations or functions of embodiments of the present invention areimplemented by firmware or software, firmware or software may beconfigured to include modules, procedures, functions, etc. forperforming the functions or operations of embodiments of the presentinvention. The firmware or software configured to perform embodiments ofthe present invention may be included in the processors 11 and 21 orstored in the memories 12 and 22 so as to be operated by the processors11 and 21.

The processor 11 of the transmitting device 10 performs coding andmodulation with respect to a signal and/or data which is scheduled bythe processor 11 or a scheduler connected to the processor 11 to betransmitted to an external device and transmits the signal and/or datato the RF unit 13. For example, the processor 11 transforms a datastream to be transmitted into K layers via demultiplexing and channelcoding, scrambling, modulation, etc. The coded data stream is alsocalled a codeword and is equivalent to a transport block which is a datablock provided by a medium access control (MAC) layer. One transportblock (TB) is encoded into one codeword and each codeword is transmittedto the receiver in the form of one or more layers. For frequencyup-conversion, the RF unit 13 may include an oscillator. The RF unit 13may include N_(t) (N_(t) being a positive integer) transmit antennas.

Signal processing of the receiving device 20 is the inverse of signalprocessing of the transmitting device 10. Under control the processor21, the RF unit 23 of the receiving device 20 receives a radio signaltransmitted by the transmitting device 10. The RF unit 23 may includeN_(r) (N_(r) being a positive integer) receive antennas and the RF unit23 performs frequency down-conversion with respect to each signalreceived via each receive antenna and restores a baseband signal. The RFunit 23 may include an oscillator for frequency down-conversion. Theprocessor 21 may perform decoding and demodulation with respect to theradio signal received via the receive antennas and restore original datatransmitted by the transmitting device 10.

Each of the RF units 13 and 23 includes one or more antennas. Theantennas serve to transmit the signals processed by the RF units 13 and23 to external devices or to receive radio signals from external devicesand to send the radio signals to the RF units 13 and 23 under control ofthe processors 11 and 21 according to one embodiment of the presentinvention. The antennas are also called antenna ports. Each antenna maybe composed of one physical antenna or a combination of more than onephysical antenna elements. The signal transmitted by each antenna is notdecomposed by the receiving device 20. A reference signal (RS)transmitted in correspondence with the antenna defines the antennaviewed from the viewpoint of the receiving device 20 and enables thereceiving device 20 to perform channel estimation of the antennaregardless of whether the channel is a single radio channel from asingle physical antenna or a composite channel from a plurality ofphysical antennal elements including the above antennas. That is, theantenna is defined such that the channel for delivering a symbol overthe antenna is derived from the channel for delivering another symbolover the same antenna. In case of the RF unit supporting a multipleinput multiple output (MIMO) function for transmitting and receivingdata using a plurality of antennas, two or more antennas may beconnected.

In the embodiments of the present invention, a UE operates as thetransmitting device 10 in uplink and operates as the receiving device 20in downlink. In the embodiments of the present invention, an eNBoperates as the receiving device 20 in uplink and operates as thetransmitting device 10 in downlink. Hereinafter, the processor, the RFunit and the memory included in the UE are respectively referred to as aUE processor, a UE RF unit and a UE memory and the processor, the RFunit and the memory included in the eNB are respectively referred to asan eNB processor, an eNB RF unit and an eNB memory.

The detailed description of the exemplary embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the exemplary embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims. Accordingly, the inventionshould not be limited to the specific embodiments described herein, butshould be accorded the broadest scope consistent with the principles andnovel features disclosed herein.

The present invention is applicable to various wireless systemssupporting narrowband communication in order to provide an IoT servicein addition to a wireless communication system for providing an IoTservice based on an LTE system.

What is claimed is:
 1. A method for a base station to transmit anarrowband synchronization signal to one or more user equipments (UEs)in a wireless communication system, the method comprising: transmittinga narrowband primary synchronization signal using a first Zadoff-Chusequence having a predetermined root index; and transmitting anarrowband secondary synchronization signal indicating a narrowband cellidentity, wherein the narrowband secondary synchronization signal isgenerated by multiplying a cover sequence, element by element, with asequence which is generated by phase shifting of a base sequence,wherein the base sequence is generated based on a second Zadoff-Chusequence having a predetermined length L in a frequency domain, whereina root index of the second Zadoff-Chu sequence is selected from among M(M<L) root indices within a range of k to k+M−1 in terms of apredetermined offset k, and wherein L, M and k are natural numbersgreater than
 1. 2. The method according to claim 1, wherein the basesequence has a length N greater than the length L by cyclic extension ofthe second Zadoff-Chu sequence having the length L, and wherein N is annatural number greater than
 1. 3. The method according to claim 2,wherein the N elements of the base sequence are transmitted in Porthogonal frequency division multiplexing (OFDM) symbols as each of Qelements of the N elements are mapped to each of the P OFDM symbols,wherein P and Q are natural numbers greater than 1, and wherein P*Q=N.4. The method according to claim 3, wherein P is 11, Q is 12 and N is132.
 5. The method according to claim 4, wherein L is 131, M is 126 andk is
 3. 6. The method according to claim 1, wherein the secondZadoff-Chu sequence is defined as:${{{Szc}\left( {u,n} \right)} = e^{j\frac{\pi\;{{un}{({n + 1})}}}{L}}},$where n=0, . . . , 130 L=131 wherein u denotes the root index of thesecond Zadoff-Chu sequence and satisfies u∈{3, . . . , 128}.
 7. Themethod according to claim 1, wherein the cover sequence is a Hadamardsequence having a length R equal to or less than L, and wherein R is anatural number greater than
 1. 8. The method according to claim 7,wherein one of four Hadamard sequences is selected as the coversequence, wherein the four Hadamard sequences include 0^(th), X-th, Y-thand Z-th Hadamard sequences having the length R, and wherein the X-th,Y-th and Z-th Hadamard sequences do not correspond to first, second andthird Hadamard sequences having the length R, and wherein X, Y and Z arenatural numbers greater than
 1. 9. The method according to claim 1,wherein the narrowband synchronization signal is transmitted in order toperform Internet of Things (IoT) communication operation through anarrowband corresponding to a part of a system bandwidth of the wirelesscommunication system.
 10. A method for a user equipment (UE) to receivea narrowband synchronization signal from a base station in a wirelesscommunication system, the method comprising: receiving a narrowbandprimary synchronization signal configured in the form of a firstZadoff-Chu sequence having a predetermined root index; and receiving anarrowband secondary synchronization signal indicating a narrowband cellidentity, wherein the narrowband secondary synchronization signal isreceived in a form of a sequence generated i) by phase shifting of abase sequence, and ii) by multiplying a cover sequence, element byelement, with the phase-shifted base sequence, wherein the base sequenceis generated based on a second Zadoff-Chu sequence having apredetermined length L in a frequency domain, wherein a root index ofthe second Zadoff-Chu sequence is selected from among M (M<L) rootindices within a range of k to k+M−1 in terms of a predetermined offsetk, and wherein L, M and k are natural numbers greater than
 1. 11. Themethod according to claim 10, wherein the base sequence has a length Ngreater than the length L by cyclic extension of the second Zadoff-Chusequence having the length L, and wherein N is a natural number greaterthan
 1. 12. The method according to claim 11, wherein the N elements ofthe base sequence are received in P orthogonal frequency divisionmultiplexing (OFDM) symbols as each of Q elements of the N elements aremapped to each of the P OFDM symbols, wherein P and Q are naturalnumbers greater than 1, and wherein P*Q=N.
 13. The method according toclaim 10, wherein the second Zadoff-Chu sequence has a form of:${{{Szc}\left( {u,n} \right)} = e^{j\frac{\pi\;{{un}{({n + 1})}}}{L}}},$where n=0, . . . , 130, L=131 wherein u denotes the root index of thesecond Zadoff-Chu sequence and satisfies u∈{3, . . . , 128}.
 14. A basestation for transmitting a narrowband synchronization signal to one ormore user equipments (UEs) in a wireless communication system, the basestation comprising: a processor configured to generate a narrowbandprimary synchronization signal using a first Zadoff-Chu sequence havinga predetermined root index and to generate a narrowband secondarysynchronization signal indicating a narrowband cell identity; and atransceiver configured to transmit the narrowband primarysynchronization signal and the narrowband secondary synchronizationsignal generated by the processor to the one or more UEs, wherein theprocessor is further configured to generate the narrowband secondarysynchronization signal by multiplying a cover sequence, element byelement, with a sequence which is generated by phase shifting of a basesequence, wherein the base sequence is generated based on a secondZadoff-Chu sequence having a predetermined length L in a frequencydomain, wherein the processor is further configured to select a rootindex of the second Zadoff-Chu sequence from among M (M<L) root indiceswithin a range of k to k+M−1 in terms of a predetermined offset k, andwherein L, M and k are natural numbers greater than
 1. 15. A userequipment (UE) for receiving a narrowband synchronization signal from abase station in a wireless communication system, the UE comprising: atransceiver configured to receive a narrowband primary synchronizationsignal configured in the form of a first Zadoff-Chu sequence having apredetermined root index and to receive a narrowband secondarysynchronization signal indicating a narrowband cell identity; and aprocessor configured to process the narrowband primary synchronizationsignal and the narrowband secondary synchronization signal received bythe transceiver, wherein the processor is further configured to processthe secondary synchronization signal in a form of a sequence generatedi) by phase shifting of a base sequence, and ii) by multiplying a coversequence, element by element, with the phase-shifted base sequence, andwherein the base sequence is generated based on a second Zadoff-Chusequence having a predetermined length L in a frequency domain, whereinthe processor is further configured to detect a root index of the secondZadoff-Chu sequence among M (M<L) root indices within a range of k tok+M−1 in terms of a predetermined offset k, and wherein L, M and k arenatural numbers greater than 1.